Native American people living in unorganized portions of the Missouri Territory had been promised that they would keep their land permanently. However, White settlers quickly broke the agreement, including most notoriously Joseph Robidoux, and demanded incorporation of settled territory into the recently formed state of Missouri that was located east of the Missouri River to the latitude of the state's northern border.

The tribes were paid $7,500 for their land. The U.S. government was to "build five comfortable houses for each tribe, break up 200 acres of land, fence 200 acres of land, furnish a farmer, blacksmith, teacher, interpreter, provide agricultural implements, furnish livestock" and a host of other small items. The tribes agreed to move to reservations west of the Missouri River in what was to become Kansas and Nebraska, today known as the Ioway Reservation and the Sac and Fox Reservation.

The western border of Missouri was established at the mouth of the Kaw River in Kansas City . The purchase extended the Missouri border in the northwest to 95 degrees 46 minutes West longitude).

On 28 March 1837, President Martin Van Buren proclaimed the Platte Purchase part of the state of Missouri, making what was the largest state in the union at that time even larger.

Current maps show the eastern border of Platte County and all counties north further east than the border between Missouri and Kansas south of the river, which no longer conforms to the mouth of the Kaw River.